Briefly, prior green roof systems typically comprise several layers of materials suitable to support vegetation on a roof. These layers are typically supplied in bulk or earthen rolls that are rolled into position on the roof.
Common types of vegetation used in green roof systems include herbs, grasses, mosses, wild plants and flowers, and other types of perennials.
A typical prior green roof system includes at least (i) a waterproofing membrane laid over the roof or roof supporting structure, (ii) based on the roof grade, a layer over the waterproofing membrane of one of: (a) a drainage layer and an overlaying blanket of root growth protection material (for a grade of approximately 2 to 5 degrees), (b) a root growth protective fleece (for a grade of approximately 6 to 10 degrees), and (c) a substrate fixing or erosion control blanket including root growth protection (for a grade of approximately 10 to 20 degrees); (iii) a layer of mineral wool or other substrate for water retention, and (iv) a top layer of vegetation growing in a fiber fleece or other suitable growing medium.
Other green roof designs include additional layers of various materials for various roof protection and vegetation growth support purposes.
It is believed that prior green roof systems of the above general type were first used in Europe approximately 20 years ago. Since that time, use of similar and derivative green roof systems has become common in many parts of Europe on commercial, institutional, industrial, and residential buildings, and interest in green roof systems is growing in the United States.
The advantages typically attributed to green roof systems include extending the roof service life; reducing heating and cooling energy costs; conserving and utilizing valuable commercial space; reducing runoff from roof surfaces; and increasing property values.
However, inspection of such prior systems also reveal the following disadvantages:                the prior systems are relatively expensive and are difficult to install, typically requiring the need for and assistance of a specially trained consultant;        the systems are not designed to be installed over an existing functional roof without the necessity of reroofing;        thus, a complete new waterproofing membrane must typically be installed before the green roof system can be used on existing buildings, resulting in additional costs;        since the green roof materials are delivered in bulk or earthen rolls, design freedom is limited, alternating designs of plants are not easily incorporated in the design of the green roof;        terracing or variations of surfaces are also not easily accomplished; and changing of the design layout after installation requires removal and destruction of the effected area and replanting with the new design;        selection of pre-growing plants in the upper fiber fleece is typically limited to low-growing plants, mosses, etc., since the fleece is supplied to the roof in rolls;        selection of pre-grown plants available is further typically limited because: the need to maintain the plants in the growing state prior to shipment results in additional costs; the demand must be estimated in advance of the installation season in order to have the pre-grown plants ready; and such estimates are typically conservative in order to prevent overstocking and spoilage if not used during that season; and        maintenance and repair to the roof is difficult and expensive; if a leak develops in the roof membrane, or if other maintenance or repair is required, the entire green roof, or at least large portions of the green roof, must be removed to locate and repair the leak or accomplish the desired maintenance; the removed green roof must then be replaced and replanted.        
Thus, it is clear there is a need for new and improved green roof systems which:                are less expensive and more easily installed than prior green roof systems;        can be installed over existing roofing materials on existing buildings, thus eliminating the need and associated cost to install completely new roofing membranes or systems prior to installation of the green roof;        provide for substantially enhanced design flexibility and freedom, including;                    the ability to change the design layout of the green roof after initial installation, and            the ability to be used either as a standalone system, or in combination with prior green roof systems                            as an original green roof layout and design including both prior systems and systems in accordance with the present invention, and                to enable repair of a prior green roof such as when a portion of the prior green roof has been removed for repairs of the building roof deck, to eliminate the current need to re-install the entire prior green roof systems after such removals or repairs; and                                                permit ease of access to desired portions of the roof for maintenance and repair without the need to destroy and then replace large portions of the green roof.        